The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
Usually, a person needing to wear spectacles and having thus a prescription filled by an ophthalmologist goes to the premise of an optician for choosing a spectacle frame. The future wearer of the spectacle frame may try several spectacle frames and finally chooses one of the tried frames. The optician orders a pair of lenses corresponding to the wearer's prescription. The lenses sent to the optician are designed and manufactured according to optical criteria.
Depending on the service provided by the lens manufacturer, the optician may have to cut the lenses to fit the spectacle frame the person has chosen or in case of “remote edging” service the optician receives the lenses already cut and only has to fit them in the spectacle frame.
The geometrical characteristics of the chosen spectacle frame can be measured very precisely by a measuring device, for example a mechanical sensor or be provided via a data base.
The geometrical characteristics of the chosen spectacle frame make it possible to provide ophthalmic lenses which fit the chosen spectacle frame, on the one hand, and the wearer prescription, on the other hand.
The lenses provider has to ensure that the provided lenses are adapted to the wearer prescription and to the chosen spectacle frame. So as to fit and be mounted in the chosen spectacle frame, the ophthalmic lens has to fulfill a number of mounting requirements. Among such mounting requirements, the thickness of the ophthalmic lens at the tie points of the ophthalmic lens to be mounted in the spectacle frame is of great importance.
Conventionally, the lens provider calculates the ophthalmic lenses based on optical criteria, in particular the wearer's prescription. So as to limit weight of the ophthalmic lens, the lens provider optimizes the lens to as to provide the thinner ophthalmic lenses as possible.
However, so as to respect the thickness requirements of the chosen spectacle frame, the lens provider is usually required to globally oversize the ophthalmic lens; thus providing ophthalmic lenses that are thicker and heavier than initially optimized by the lens provider.